The principal investigator recently developed a new method for isolating fresh relatively pure type II cells (TII) that can be used to study the regulation of surfactant phosphatidylcholine (PC) synthesis in the developing lung. In the lung the rate limiting reaction in PC synthesis is catalyzed by cholinephosphate cytidylyltransferase (CTYase). This complex enzyme which is relatively inactive in cytosol, is activated by association with microsomal membranes. Understanding the mechanism(s) regulating CTYase activation at birth and the response to hormones is of major importance for the development of preventive therapies for Respiratory Distress Syndrome (RDS), a condition of surfactant deficiency in premature infants. Recent observations of the principal investigator confirm that microsomal enzyme activation is a key step in the lung's adaptation following birth: 1) microsomal CYTase activity expressed by TII cells rapidly increases six fold following birth to greater than adult levels; and 2) microsomal enzyme in fetal TII cells is stimulated in vivo by maternal dexamethasone (dex) administrator or in vitro dex treatment of cultured cells. The goal of this proposal is to elucidate the mechanisms responsible for CYTase activation in the perinatal period. Many membrane bound enzymes are regulated by the membrane lipid environment. Although evidence suggests that membrane lipid is required for CYTase activation, the mechanisms by which membrane lipid modification affect CYTase have not been investigated. The project's hypothesis is that CYTase activity in TII cells is regulated by changes in cellular fatty acids. Possible mechanisms that will be studied are: 1) modification of the fatty acid composition of membrane phospholipids alters the activation state of the microsomal CYTase enzyme and/or promotes enzyme binding to membranes and 2) fatty acid modulation of glucocorticoid-receptor interaction alters the CYTase response to glucocorticoids. Complementary studies will be conducted involving dietary fat alteration of pregnant and lactating rats, fatty acid supplementation of cultured type II cells, and phospholipid fatty acid modifications of isolated microsomes. These studies will focus on how altering chain length and the number and placement of double bonds in membrane phospholipid fatty acids affect activity of microsomal CYTase during lung development. Specifically, the n-6 and n-3 (marine oil) polyunsaturated fatty acids and the essential fatty acid linoleic acid will be evaluated. Fatty acid modulation of glucocorticoid-receptor interactions in TII cells and the effects of fatty acids and dex on CYTase activity in cultured TII cells will be examined. Overall effects on intermediates in PC synthesis will be assessed by pulse change studies. Changes in microsome phospholipid fatty acid composition will be determined by gas chromatography. CYTase activity will be assayed in cellular subfractions. Characteristics of glucocorticord receptor binding will be assessed using [3H] triamcinolone acetonide. Results of this study will contribute significantly to our understanding of the role of maternal nutrition in fetal lung development.